Bovine somatomedin (sulfation factor) from approximately four hundred l of blood has been purified ca. 20,000-fold relative to our laboratory reference serum. This partially purified preparation augments the biosynthesis of RNA, protein and chondroitin sulfate in the in vivtro costal cartilage assay system. The active principle obtained at this stage exists as a large molecule (greater than 12,000 MW) as determined by molecular sieve chromatography and analytical dialysis. Bovine blood is being purified to this point routinely in order to accumulate sufficient hormone for further purification. Results of initial studies suggest that urine may possibly qualify as an alternate source of somatomedin. To date stimulation of sulfation activities has been observed in urine preparations. As with the somatomedin activity noted in serum, the active principle present in urine exists as a large (greater than 12,000MW) component(s). The presence of other metabolic activities inurine which are associated with somatomedin are being studied presently.